Conventionally employed sodium (Na) flux processes, which grow gallium nitride crystal in an Na flux, can grow a GaN single crystal at a pressure of about 5 MPa and at a relatively low temperature of 600° C. to 800° C.
As disclosed in, for example, the below-described Patent Documents 1 to 5, in conventional methods for producing a group III nitride based compound semiconductor crystal, the crystal is grown through the flux process. Such a conventional production method generally employs, as a base substrate (seed crystal), a template formed by successively providing, on a sapphire substrate, a buffer layer and a semiconductor layer (e.g., a single-crystal GaN layer); a GaN single-crystal self-standing substrate; or a similar substrate.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. H11-060394
[Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 2001-058900
[Patent Document 3] Japanese Patent Application Laid-Open (kokai) No. 2001-064097
[Patent Document 4] Japanese Patent Application Laid-Open (kokai) No. 2004-292286
[Patent Document 5] Japanese Patent Application Laid-Open (kokai) No. 2004-300024